playermgr: make event loop for getting player callback

playermgr: make event loop for getting player callback

Since callback of player is called from another thread,
we can't use efl object that is made from main thread.
(EFL can't guarantee thread safe)
The main thread check the events list(for callback) periodically,
and call real callback when get the events.

Change-Id: Ia24754c78ad5dd751e174e6c69273ec35aaea652
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>